1. Field of the Invention
The present invention is directed to a rare earth magnetostrictive driven flextensional transducer and, more particularly, to a flextensional transducer in which rare earth drive rods are biased by rare earth magnets.
2. Description of the Prior Art
Flextensional transducers are a class of mechanical amplifiers that use a drive bar to expand a pseudo elliptical shell, having a minor to major axis ratio of about 0.4, in the direction of the major axis. The expansion by the shell along major axis causes the shell to deform or deflect along the minor axis. The deflection associated with the minor axis is magnified and out of phase with the expansion along the major axis and causes sound waves to be produced. A prior art example of a flextensional shell 10 driven by a ceramic bar 11 is illustrated in FIG. 1. When the electrodes (not shown) of the individual blocks (not shown), stacked to form the ceramic bar 11, are excited with a driving voltage, the ceramic bar expands or contracts along the Y axis causing the shell 10 to contract or expand, respectively, along the X axis. Such a ceramic transducer experiences high loss at the elevated temperatures associated with high driving levels.
FIG. 2 illustrates a prior art folded horn transducer in which the bell-shaped housing 20 is driven by rare earth magnetostrictive rods 21 excited by solenoids 22. The solenoids are wired in series and magnetically coupled by magnetic couplers 23 so that a return flux path is created. The rods are mechanically biased using stress plates 24 and stress bolts 25. The housing 20 includes a gap 26 which allows each housing 20 to ring like a bell. The transmitting voltage response of the folded horn transducer of FIG. 2 is illustrated in FIG. 3A. If ceramic rods are substituted for the rare earth rods 21, a transmitting voltage response as illustrated in FIG. 3B will result. This type of transducer, as illustrated by FIGS. 3A and 3B, has relatively low output levels.